RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Patent App. No. 62/578,916, filed October 30, 2017, which is incorporated herein by reference.

GOVERNMENT INTEREST

This invention was made with government support under Grant No. EEC- 1160483 awarded by the National Science Foundation. The government has certain rights in the invention.

BACKGROUND

Self-powered quartz watches have been in existence for approximately 30 years. These watches generate power by means of an eccentric rotor that rotates when the wearer's wrist moves. This rotor drives a gear train, which in turn drives a generator. This generator works well for certain types of motion but is not very well suited to walking or to being worn on the upper arm, torso or waist.

Other inertial devices use linear rotor or "proof mass" motion to harvest electrical energy, but this has limited power output because of the limited internal travel range of the proof mass. In order to overcome this limitation of linear motion-based harvesters, devices with a rotational proof mass have been adopted by researchers and the wristwatch industry. These devices utilize an eccentric rotor structure that couples the kinetic energy generated by human walking or running into a transduction mechanism. During normal walking motion, the proof mass rotational amplitude of such eccentric rotor structures is quite small. Notably, larger rotational amplitudes will result in higher power output.

Due to improvements in manufacturing technologies, most electronic devices and sensors have become miniaturized in size and require a relatively low power consumption. Wearable consumer electronics (e.g., smartwatch, lifestyle tracker band, smart training shoes etc.) typically contain one or more sensors to track a user's daily activities which are usually powered by electrochemical batteries (e.g., Li-ion, Li-Po). Although they exhibit high energy density, these batteries have a limited life span and require periodic charging, which is sometimes inconvenient or even impossible. Kinetic energy harvesting from motion of a person (or animal) can be a good alternative to overcome these power limitations, because significant power can be generated from human body motion, for instance. However, when compared to other kinetic energy sources, harvesting power from human body motion is challenging due to its low-frequency (below 5 Hz) and random characteristics.

SUMMARY

The present disclosure sets forth an energy harvester device comprising a support structure, an eccentrically weighted rotor rotatably coupled to the support structure, a rotor movement limiter mechanism (e.g., rotational spring) coupled to the support structure and coupled to the eccentrically weighted rotor, and a transducer operably coupled to the eccentrically weighted rotor for harvesting electrical energy upon rotation of the eccentrically weighted rotor about the support structure. The rotor movement limiter mechanism can be operable to maintain the eccentrically weighted rotor in a generally upward position with respect to gravity when the energy harvester device is worn by a user in a standard use orientation.

In one example, the present disclosure sets forth a system for harvesting electrical energy from an energy harvester device worn by a user comprising the energy harvester device including a user attachment mechanism having a standard use orientation, such that the energy harvester device experiences a gravitational force while being moved along with the user. The energy harvester device can comprise a support structure, an eccentrically weighted rotor rotatably coupled to the support structure, a rotor movement limiter mechanism coupled to the support structure and coupled to the eccentrically weighted rotor; and a transducer operably coupled to the eccentrically weighted rotor. The rotor movement limiter mechanism maintains the eccentrically weighted rotor in a generally upward position with respect to the standard use orientation to resist the gravitational force while the rotor rotates about the support structure to harvest electrical energy via the transducer.

The present disclosure sets forth a method for harvesting electrical energy by wearing the energy harvester device, and that can comprise moving in anthropomorphic motions such that the eccentrically weighted rotor rotates in opposite direction, and with at least some assistance from a nonlinear restoring torque provided by the rotor movement limiter mechanism in the form of a rotational coil spring upon the release of stored energy.

There has thus been outlined, rather broadly, the more important features of the invention so that the detailed description thereof that follows may be better understood, and so that the present contribution to the art may be better appreciated. Other features of the present invention will become clearer from the following detailed description of the invention, taken with the accompanying drawings and claims, or may be learned by the practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an energy harvester device having an anti- gravitational spring in the form of a rotational spring, in accordance with an example of the present disclosure.

FIG. 2A is a schematic representation of an energy harvester device in a default position being a standard use orientation with respect to gravity and as worn by a use, in accordance with an example of the present disclosure.

FIG. 2B is a schematic representation of the energy harvester device of FIG. 2A, having an eccentrically weighted rotor rotated to a first position upon a first movement of the user, in accordance with an example of the present disclosure.

FIG. 2C is a schematic representation of the energy harvester device of FIG. 2A, showing the eccentrically weighted rotor rotated to a second position upon a second movement of the user, in accordance with an example of the present disclosure.

FIG. 3A is a graph of power output vs. electrical damping coefficient from an energy harvester device, in accordance with an example of the present disclosure.

FIG. 3B is a graph of power output vs. spring constant from an energy harvester device during walking of a human, in accordance with an example of the present disclosure.

FIG. 3C is a graph of electrical damping and spring stiffness resulted from the input data of five subjects for a traditional rotor without a spring, and for an energy harvester device having an eccentrically weighted rotor and an anti-gravitational spring according to the present disclosure.

FIG. 3D is a graph of power outputs resulted from the input data of five subjects for a traditional rotor without a spring, and for an energy harvester device having an eccentrically weighted rotor and an anti-gravitational spring according to the present disclosure.

FIG. 3E is a graph of power vs. spring stiffness for a particular anti-gravitational spring, in accordance with an example of the present disclosure.

FIG. 4A is an isometric view of an energy harvester device, in accordance with an example of the present disclosure.

FIG. 4B is a partially exploded view of the energy harvester device of FIG. 4 A. FIG. 4C is a side cross sectional view of the energy harvester device of FIG. 4A, and taken along lines 4C-4C.

FIG. 4D is a circuit drawing including the energy harvester device of FIG. 4A, in accordance with an example of the present disclosure.

FIG. 4E is a graph of power vs. spring stiffness resulting from movement of the energy harvester device of FIG. 4 A.

FIG. 4F is a graph of power vs. spring stiffness resulting from movement of the energy harvester device of FIG. 4A and at full flux, and as an average for a plurality of humans wearing the energy harvester device while walking.

FIG. 4G is a graph of power vs. spring stiffness resulting from movement of the energy harvester device of FIG. 4A and at half flux, and as an average for a plurality of humans wearing the energy harvester device while walking.

FIG. 5A is an isometric view of an energy harvester device, in accordance with an example of the present disclosure.

FIG. 5B is a partially exploded view of the energy harvester device of FIG. 5 A. FIG. 5C is a side cross sectional view of the energy harvester device of FIG. 5A, and taken along lines 5C-5C.

FIG. 6A is an isometric view of an energy harvester device, in accordance with an example of the present disclosure. FIG. 6B is an isometric cross sectional view of the energy harvester device of FIG. 6 A, and taken along lines 6B-6B.

FIG. 6C is a graph showing power results for ten subjects walking at 2.5 mph.

FIG. 6D is a graph showing power results for ten subjects walking at 3.5 mph.

FIG. 6E is a graph showing power results for ten subjects jogging at 5.5 mph.

FIG. 7 A is an isometric view of an energy harvester device, in accordance with an example of the present disclosure.

FIG. 7B is a partially exploded view of the energy harvester device of FIG. 7 A.

FIG. 7C is a side cross sectional view of the energy harvester device of FIG. 7A, and taken along lines 7C-7C.

FIG. 8A is an isometric view of an energy harvester device, in accordance with an example of the present disclosure.

FIG. 8B is a partially exploded view of the energy harvester device of FIG. 8 A, in accordance with an example of the present disclosure.

FIG. 9A is a schematic representation of an energy harvester device having an anti- gravitational spring in the form of a magnetic latching system, and an eccentrically weighted rotor in a first latched position, in accordance with an example of the present disclosure.

FIG. 9B is a schematic representation of the energy harvester device in a second latched position, in accordance with an example of the present disclosure.

These drawings are provided to illustrate various aspects of the invention and are not intended to be limiting of the scope in terms of dimensions, materials, configurations, arrangements or proportions unless otherwise limited by the claims. DETAILED DESCRIPTION

While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be realized and that various changes to the invention may be made without departing from the spirit and scope of the present invention. Thus, the following more detailed description of the embodiments of the present invention is not intended to limit the scope of the invention, as claimed, but is presented for purposes of illustration only and not limitation to describe the features and characteristics of the present invention, to set forth the best mode of operation of the invention, and to sufficiently enable one skilled in the art to practice the invention. Accordingly, the scope of the present invention is to be defined solely by the appended claims.

Definitions

In describing and claiming the present invention, the following terminology will be used.

The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a spring" includes reference to one or more of such elements and reference to "subjecting" refers to one or more such steps.

As used herein with respect to an identified property or circumstance, "substantially" refers to a degree of deviation that is sufficiently small so as to not measurably detract from the identified property or circumstance. The exact degree of deviation allowable may in some cases depend on the specific context.

As used herein, "adjacent" refers to the proximity of two structures or elements. Particularly, elements that are identified as being "adjacent" may be either abutting or connected. Such elements may also be near or close to each other without necessarily contacting each other. The exact degree of proximity may in some cases depend on the specific context.

As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.

As used herein, the term "at least one of is intended to be synonymous with "one or more of." For example, "at least one of A, B and C" explicitly includes only A, only B, only C, and combinations of each.

As used herein, the term "about" is used to provide flexibility and imprecision associated with a given term, metric or value. The degree of flexibility for a particular variable can be readily determined by one skilled in the art. However, unless otherwise enunciated, the term "about" generally connotes flexibility of less than 2%, and most often less than 1%, and in some cases less than 0.01%.

Concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and subrange is explicitly recited. For example, a numerical range of about 1 to about 4.5 should be interpreted to include not only the explicitly recited limits of 1 to about 4.5, but also to include individual numerals such as 2, 3, 4, and sub-ranges such as 1 to 3, 2 to 4, etc. The same principle applies to ranges reciting only one numerical value, such as "less than about 4.5," which should be interpreted to include all of the above-recited values and ranges. Further, such an interpretation should apply regardless of the breadth of the range or the characteristic being described.

Any steps recited in any method or process claims may be executed in any order and are not limited to the order presented in the claims. Means-plus-function or step-plus- function limitations will only be employed where for a specific claim limitation all of the following conditions are present in that limitation: a) "means for" or "step for" is expressly recited; and b) a corresponding function is expressly recited. The structure, material or acts that support the means-plus function are expressly recited in the description herein. Accordingly, the scope of the invention should be determined solely by the appended claims and their legal equivalents, rather than by the descriptions and examples given herein.

Kinetic Energy Harvesting using Improved Eccentric Rotor Architecture for

Wearable Sensors

FIGS. 1-2C illustrate an energy harvester device 100 that can be incorporated with an electronics assembly or device, such as a wearable electronics device, for powering electronics components or a battery of the wearable electronics device. As an overview, the energy harvester device 100 can comprise a reference frame or support structure 102, and an eccentrically weighted rotor 104 rotatably coupled to the support structure 102 (e.g., by a shaft). The eccentrically weighted rotor 104 can include a mass 105 disposed around a radial section of the eccentrically weighted rotor 104, as shown, to generate a rotor that is eccentrically weighted. The energy harvester device 100 can comprise a rotor movement limiter mechanism, such as a rotational coil spring 106 can be operably coupled to the support structure 104, such as a rotational torsional spring as shown, and as further exemplified below (see e.g., the examples of FIGS. 4B, 5B, 6B, and 7B). Although not shown in FIGS. 1-2C, a transducer can be operably coupled to, and/or defined in part by, the eccentrically weighted rotor 104 for harvesting electrical energy upon rotation of the eccentrically weighted rotor 104 relative the support structure 102. In one example, the eccentrically weighted rotor at least partially defines the transducer, and the transducer can comprise a substrate supporting a plurality of coils, and the eccentrically weighted rotor can comprise a mass coupled to a portion of the substrate. Thus, the substrate and coils rotate with the mass during movement of the user. As will be detailed below in various examples, a particular transducer can take many shapes and forms, and can be part of the eccentrically weighted rotor, and/or the anti-gravitational spring, and/or the support structure, and/or the bearings or other components of the device 100. Notably, the rotational coil spring 106 can be configured to or operable to maintain or balance the eccentrically weighted rotor 104 in a generally upward position with respect to gravity G when the energy harvester device 100 is worn by a user in a standard use orientation O, as illustrated in the orientation of FIG. 2A, in one example.

Rotation of the eccentrically weighted rotor 104 is constrained to motion in the XY plane. Therefore, the governing equations of such motion in the XY plane are

(ø_ + φ, )+ (t) + 1> = F t s F.J cos (2) where m, /, and IQ are the mass (i.e., the eccentrically weighted rotor 104), eccentric distance and moment of inertia of the rotor 104, respectively. X and Ϋ are the input accelerations to the system working along X and Y coordinates, respectively. In equation (2), D _m and D _e are the mechanical and electrical damping coefficients, respectively. And, F _x , F _y and g _x , g _y are the forces from the reference frame (support structure) and gravity acting on the rotor respectively in the corresponding coordinate. And, φ _ζ is the angular displacement of the rotor relative to the reference frame (support structure).

When including a rotational spring (e.g., 106) having the rotational spring constant, k _sp , the rotational displacement of a particular energy harvest device will be f _n I SIB ψ„ - F cos , (3)

The relative angular displacement/velocity of the eccentrically weighted rotor can be obtained by solving the governing equations, which determines the power output as p = I) # 4)

In one experiment, to simulate real human walking, a pseudo-walking signal can be used in the model and defined as

ISO

The swing amplitude can be ±12.5° and the swing frequency can be 1.2 Hz. This pseudo- walking signal can be generated based on the data collected from real human motion.

In operation, this configuration can dramatically increase the amount of electrical energy harvested by the energy harvester device 100, as compared to a similarly constructed conventional rotor generator known in the art (i.e., one not having a spring, and that is free to rotate 360 degrees in either direction), which is exemplified in the data comparisons shown in the graphs of FIGS. 3 A, 3C, and 3D. More specifically, FIG. 2A shows the energy harvester device 100 in the standard use orientation O, such that a gravitational force G is acting on the energy harvester device 100 in a generally downward manner. For instance, the energy harvester device 100 can be worn (as part of a wearable electronics device) on the left wrist of a user in the zero displacement position or orientation shown in FIG. 2A (or the energy harvester devices exemplified herein can be worn on or around the torso/chest, on suspenders, on a belt, in clothing, in shoes, etc., where the rotor is balanced upwardly by a spring). Typically, a corresponding device housing can encompass the energy harvester device 100 in a desired orientation. More specifically a user interface which is integrated or attached to the housing can be used to secure the device to a user. The user interface can include, but is not limited to, a strap, a clip, a loop, a band, adhesive, and the like. Furthermore, the device could be secured to the user by being placed in a special purpose pocket or pouch in clothing or secured to a shoe for example. The user interface can then orient the energy harvester device in the standard use orientation. Alternatively, the housing can include a marker which indicates an "up" position (e.g. an arrow, "up" label, tick, etc) in order to assist a user in proper wearing positions. In the example of FIG. 2 A, one end of the rotational coil spring 106 can be attached to a shaft 108 of the energy harvester device 100, which is fixed to the support structure 102 (see also FIG. 7 A). The other end of the anti-gravitational spring 106 can be attached to a portion of the eccentrically weighted rotor 104 in a manner so that a default position of the eccentrically weighted rotor 104 is generally upward with respect to the gravitational force G. Said another way, a center of mass M of the eccentrically weighted rotor 104 can be maintained to be above a 180 degree plane P of the support structure 102 that extends horizontally or laterally through the device 100, as shown in FIG. 2 A, by the biasing or balancing provided by the rotational coil spring 106. Thus, the rotational coil spring 106 can be configured to balance, maintain or bias the eccentrically weighted rotor 104 in a rest position that provides an unstable equilibrium position of the eccentrically weighted rotor 104, which can be a generally upward position with respect to gravity G when the energy harvester device is worn by a user in the standard use orientation O. This configuration can increase the amplitude of oscillations, and therefore the power output of the energy harvester device, as should be appreciated from the present disclosure and the examples provided herein.

Note that the winding direction of the spring 106 may not be relevant, because it can be wound in either direction while still balancing or maintaining the upward orientation of the rotor 104. Also, the rotational coil spring 106 can be a linear coiled spring such as those made of spring steel, Be-Cu alloys, or other standard or known spring materials. In one alternative, the spring can be a non-linear spring, such as a stiffening or softening spring. Optionally, magnets may be added to the rotor and/or support structure to create non-linear motion and a magnetic spring effect. For example, one or more magnets can be attached to the moving rotor that are repulsed by one or more corresponding magnets attached to the housing. As the rotor magnets approach a corresponding magnet on the housing, a repulsive magnetic force tends to push the rotor away in much the same way as a spring pushes the rotor to a nominal upward rest position. An example is similar to that illustrated in FIG. 9A-9B except with poles reversed to create repulsive force instead of attractive force. Similar to a spring, the magnetic interaction force is a function of the rotor displacement. However, this magnetic interaction force would generally be a nonlinear function of the angular displacement of the rotor (e.g. force varies with angular displacement).

More particularly regarding operation, assume that a user is wearing the energy harvester device 100 on a left wrist, and is walking (e.g., an anthropomorphic motion) such that the left wrist swings upwardly during such movement of the user. Because of a gravitational force acting on the eccentrically weighted rotor 104, the eccentrically weighted rotor 104 will rotate clockwise to the position shown in FIG. 2B, such as +25 degrees from the y-axis. Accordingly, in response to such rotational movement of the eccentrically weighted rotor 104, the rotational coil spring 106 will compress and store energy. Then, when the user swings the left wrist downwardly in the opposite direction during another gait movement, at some point in time a gravitational force will cause the eccentrically weighted rotor 104 to initially rotate in the counter clockwise direction, while the rotational coil spring 106 releases its stored energy to apply a torque force that combines with the gravitational force to rotate the eccentrically weighted rotor 104 to the left to the position shown in FIG. 2C, approximately -25 degrees from the y-axis (note that the degree of rotation depends on a variety of factors, as detailed below). Accordingly, multiple successive movements of the user during walking, for instance, will cause the eccentrically weighted rotor 104 to oscillate back and forth, while taking advantage of the additional energy released by the rotational coil spring 106 to assist to rotate the eccentrically weighted rotor 104. In this way, the spring 106 exhibits a nonlinear restoring torque due to the acceleration of gravity acting on the eccentrically weighted rotor 104, such that the restoring torque somewhat acts as a softening spring.

Such structure and functionality described regarding FIGS. 1-2C (and other examples discussed herein) can improve or increase the amount of electrical energy harvested by up to 300 percent, or even more in some cases (see below). In one example, 400 μ\Υ can be produced by a particular energy harvester device, while a comparable conventional rotor generator may produce only 130 μ\Υ, for instance.

Note that the rest position of the eccentrically weighted rotor 104 may be generally vertical at 2π (i.e., positioned so that the center of mass M intersects the y-axis), or the rest position may be slightly "off vertical", such as shown in FIG. 2A where the center of mass M is approximately +8 degrees off vertical from the y-axis. The rest position may vary from vertical, such as anywhere from +/- 1 to 10 degrees, for example, or more in some cases. This "off-axis" configuration positions the eccentrically weighted rotor in somewhat of a "sagging position" slightly to the right of vertical (in FIG. 2A), so that the eccentrically weighted rotor 104 can bounce back-and-forth from this position across the y-axis, such as +/-15-25 degrees back-and-forth depending on the degree of rotation (i.e., based on movement of user). The result is an increase in the amplitude of oscillations of the eccentrically weighted rotor 104. This also provides the benefit of increasing the frequency band of the eccentrically weighted rotor 104, which helps to accommodate different types of anthropomorphic motions of different types of users because of the nonlinear or double-well oscillation provided by "sagging" the eccentrically weighted rotor 104 to one side of the y-axis.

Note that some energy harvester devices of the present disclosure can be designed so that the eccentrically weighted rotor can oscillate up to +/-45 degrees (i.e., a 90 degree sweep), but can be larger than that in some application, such as +/-90 degrees or more. Further note that a particular eccentrically weighted rotor may not oscillate across the y- axis (like the example of FIGS. 2A-2C), but may instead have a zero point displacement position at about +25 degrees from the y-axis, for instance, and then only oscillate +/- 10 degrees from such zero point displacement position.

One advantage of incorporating a spring with an eccentrically weighted rotor, such as in the various examples discussed herein, is that it effectively harvests energy by multidirectional vibrations. In other words, a particular energy harvester device can effectively harvest motion along two linear axes. A particular eccentrically weighted rotor, suspended by a rotational spring, can enhance the mechanical energy captured from low and random frequencies. Some of the variables for designing a particular energy harvester device include electrical damping coefficients, spring constants, bias of walking signal, eccentric rotor shape and material, which can be selected to maximize the power generation. To compare with the conventional or known eccentric rotor, a particular energy harvester of the present disclosure is shown to have generated doubled average power output than the conventional one under the optimal electrical damping and spring constant, and for walking data measured from 30 different subjects wearing the particular energy harvester device.

As mentioned above, FIG. 3A is a graph of electrical damping vs. power for an example energy harvester device of the present disclosure (upper line), and for a comparable conventional rotor generator (lower line). This illustrates that a particular energy harvester having a spring coupled to a rotor is capable generating 86.4% higher power (313.9 μ\Υ) than the power (168.4 μ\Υ) generated by a comparable energy harvester not having a spring. The eccentrically weighted rotor can be tungsten having 12.6 mm radius and 2 mm thickness, or other dense metal such as brass. To achieve these maximum power values, an optimum level of electrical damping coefficient can be used, which can be found to be 0.26>< 10 ^"5 N m s/rad and l x lO ^"5 N m s/rad for the conventional "unsprung rotor" and for the present "sprung rotor", respectively.

As can be appreciated from the graph of FIG. 3B, for a particular energy harvester device (e.g., 100) and in response to a gait cycle of a particular subject/user wearing the energy harvester device, a maximum power output can reach approximately 310 μ\Υ. This illustrates that the maximum power can be generated when the optimal spring constant of the sprung rotor can be 2.78>< 10 ^"4 N m/rad.

An inertial measurement platform can be used to measure input data (linear acceleration and rotational rate) from five subjects during walking, wearing a particular energy harvester device on their wrists (right hand). Gyroscopic data can be used to determine the gravitational force in X-Y plane by the orientation calculated. A Pattern Search (PS) optimization routine can be employed in order to determine the values of the energy harvester device design parameters. An objective function can be formed by virtue of the output of an ordinary differential equations solver, which solved Eqs. (2) and (3) using candidate solution values, returning the power dissipated in the electrical damper. Candidate solutions are two-dimensional, and are comprised of the design variables - the electrical damping coefficient and the rotational spring constant. As can be appreciated from the graph of FIG. 3C, showing optimal electrical damping and spring stiffness resulted from the input data of five subjects/users wearing a particular energy harvester device ("spring rotors"), the electrical damping (and consequently power output) is greater for each user as compared to comparable conventional rotor generators ("unspring rotors") worn by each user. This is also illustrated in the data shown in FIG. 3D for the same five subjects/users and experimental data results.

In one example, the rotor movement limiter mechanism comprises a rotational coil spring having a spring stiffness value sufficient to bias the eccentrically weighted rotor in an unstable dynamic equilibrium rest position that is upward with respect to gravity, such that the rotational spring is operable to restrict rotational movement of the eccentrically weighted rotor in 180 degrees or less. In one example, the rotor movement limiter mechanism comprises a rotational coil spring having one end fixed to the support structure and the other end fixed to the eccentrically weighted rotor, such that the rotational coil spring maintains the eccentrically weighted rotor in a zero displacement position that defines an unstable dynamic equilibrium rest position of the eccentrically weighted rotor that is between 1 and 10 degrees relative to a y-axis of the energy harvester device, and where the y-axis is generally vertically oriented with respect to gravity. In one example, the rotor movement limiter mechanism comprises a spring having a spring stiffness value sufficient to maintain the center of mass of the eccentrically weighted rotor above a 180 degree horizontal plane that extends laterally through the energy harvester device.

FIG. 3E shows data of power vs. spring stiffness for a particular rotational coil spring of an example energy harvester device. Notably, a particular rotational spring can be designed to have a spring stiffness defined at point A, such that the eccentrically weighted rotor is balanced by the rotational spring to be at a zero point displacement rest position to one side of the y-axis (e.g., FIG. 2A). In this way, the eccentrically weighted rotor can bounce back-and-forth about the vertical position (i.e. the y-axis), which increases the amplitude of the oscillations. Another particular rotational spring of the present disclosure can be designed to have a spring stiffness defined at point B, which is proximate the peak of the first hump or curve on FIG. 3E. In this case, as the spring is less stiff, the rotor rest position is further to one side of the y-axis compared to the spring of point A. For a spring of point B, the eccentrically weighted rotor can bounce back and forth about its rest position, but always on one side of the y-axis. In this way, the amplitude of the oscillations is increased compared to an eccentric rotor with no spring, but not as much as the rotational spring represented by point A. As a general rule, a spring stiffness within about ±30%, or within about ±15 %, and preferably within about ±5% of the local spring stiffness maximum (B) can be desirable.

FIGS. 4A-4C show an energy harvester device 400 in accordance with an example of the present disclosure, and FIGS. 4D-4F show certain aspects and data derived from operating or using the energy harvester device 400 (i.e., worn by users in motion). The energy harvester device 400 can comprise a support structure 402 that includes a first metal backing plate 412a and a second metal backing plate 412b, and a support body 417 formed as a ring shaped body that supports and retains the first and second metal backing plates 412a and 412b. The first and second metal backing plates 412a and 412b can be circular shaped disks or plates comprised of a metallic material, such as iron, steel, metal alloy, etc. The support structure 402 can further comprise a central support plate 416 coupled to a central opening 418 of the second metal backing plate 412b (see FIG. 4C). As shown best in FIG. 4B, an eccentrically weighted rotor 404 can be rotatably coupled to the central support plate 416 of the support structure 402 by a shaft 420, and the shaft 420 can be fixed or attached through an aperture 422 of the central support plate 416 (see also FIG. 4C).

As best shown in FIG. 4C, a pair of ball bearings 424 (or at least one bearing) can rotatably couple the shaft 420 to the eccentrically weighted rotor 404. Further to this rotation interface, the eccentrically weighted rotor 404 can comprise a central rotor body 426 rotatably interfaced to the ball bearings 424 to facilitate rotation of the eccentrically weighted rotor 404. The eccentrically weighted rotor 404 can further comprise a rotor substrate 428 (e.g., PCB board) having a central aperture 435 that receives and is supported by the central rotor body 426. The rotor substrate 428 can support or comprise a plurality of rotor coils 430 (i.e., left and right wound coils), which can each be received or supported by coil support openings 432 formed radially in an array around the rotor substrate 428. The eccentrically weighted rotor 404 can further comprise a mass 405, such as a curved rod or shaft or body formed of tungsten, brass, etc., disposed around a radial section of the rotor substrate 428, which provides a rotor that is eccentrically weighted.

The energy harvester device 400 can comprise a rotor movement limiter mechanism, such as a rotational coil spring 406 having one end 434a coupled to a hole (not shown) in the stator substrate 428 of the eccentrically weighted rotor 404, and the other end 434b coupled to a hole 437 in the first metal backing plate 412b. As similarly and generically exemplified in FIGS. 1-2C, the rotational coil spring 406 can be operable to maintain or bias the eccentrically weighted rotor 404 in an upward position with respect to gravity when worn by a user in a standard use orientation. This includes the functionality and benefits described herein regarding incorporating a spring in this manner to maintain or balance the eccentrically weighted rotor 404 in an upward position to provide an unstable equilibrium position of the eccentrically weighted rotor 404.

In one example, the support structure comprises a first metal backing plate and a second metal backing plate opposing each other, and the transducer can comprise a plurality of permanent stator magnets attached to the first metal backing plate, such that the permanent stator magnets are situated between respective coils and the first metal backing plate. For example, the energy harvester device 400 can further comprise a plurality of permanent stator magnets 436 attached to an inner planar surface of the first metal backing plate 412a, such that the permanent stator magnets 436 (having alternating polarity) are situated between respective rotor coils 430 and the first metal backing plate 412a, as best shown in FIG. 4C. This configuration provides a first air gap Al located between the permanent stator magnets 436 and respective coils 430, and a second air gap Al between the rotor coils and the second metal backing plate 412b. Thus, a transducer 448 of the device 400 includes only two air gaps (Al, A2) between the permanent stator magnets 436 and the rotor coils 430, which maximizes an electromagnetic damping value and minimizes a profile size of the energy harvester device. However, in this configuration the coils are part of or physically attached to the rotor, and therefore, are moving together with the rotor. This provides a relatively thin, compact energy harvester device 400 because of the reduction of air gaps being just two air gaps.

The transducer 448 can include or comprise a number of components that cooperate to transfer and harvest electrical energy from the energy harvester device 400. With reference to FIG. 4D, a generator of the energy harvester device 400 can include an AC voltage source generated by induction in the rotor coils 430 (Lcoils and Rcoils) due to rotational motion of the stator magnets 436 relative to the rotor coils 430. The rotor coils 430 can be electrically coupled together in series, and electrically coupled to the rotational coil spring 406 to an electrical load (e.g., battery, electronics component, etc.). At the other side of the circuit of FIG. 4D, the rotor coils 430 can be electrically coupled to the bearings 424. The configuration in which the rotor coils are coupled to the rotational spring on one side and to a bearing on the other side enables a smaller configuration with only two airgaps, and therefore, a larger electrical damping. Therefore, as the eccentrically weighted rotor 404 rotates, the rotor substrate 428 and the rotor coils 430 rotate relative to the permanent stator magnets 436, which generates an electromagnetic damping effect that converts mechanical energy to electrical energy via induction to generate an AC voltage source, which is then transferred via the rotational coil spring 406 and the ball bearings 424 to supply power to the electrical load. This configuration is advantageous over prior systems that require slip rings to transfer electrical energy from coils, which contributes to losses, impedance, etc.

In one example, as shown schematically in FIG. 4D, a controller 450 can be electrically coupled to the plurality of rotor coils 430 to control switching of at least one pair of opposing rotor coils 430 for facilitating variable electromagnetic damping. Thus, a plurality of switches 452 can be operably coupled between the controller 450 and respective rotor coils 430 for facilitating switching on/off of one or more pairs of rotor coils, as controlled by the controller 450. A sensor (not shown) can be included with the circuit drawing of FIG. 4D (e.g., in series with the load) for sensing a voltage generated by the energy harvester device. If the sensed voltage is below a desired or maximum threshold voltage, then the controller 450 can be programmed to turn off one or more pairs of coils to vary the electromagnetic damping of the generator, which can maximize power output in some cases. Varying electromagnetic damping in this manner provides the ability to change the electromagnetic damping for different types of user motion, such as when walking vs. running, to maximize power output for a particular activity.

The graph of FIG. 4E shows data of power vs. spring stiffness resulting from experiments performed using the energy harvester device 400. The graph of FIG. 4G shows an average curve for power vs. spring stiffness generated from the measured motion profile of the wrist of 10 different subjects walking at 3.5 mph for energy harvester device 500 (FIG. 5A). The graph of FIG. 4F shows an average curve for power vs. spring stiffness generated from the measured motion profile of the wrist of 10 different subjects walking at 3.5 mph for an energy harvester implementation with the same structure as 500, but 50% of the size of the device that generated the data shown in FIG 4G. In one example, spring stiffness for device 400 is 1.15e-4 (0.0001 15) N-m/rad. In another example, for device 500 spring stiffnesses from 0.4e-4 to 4e-4 N-m/rad such as: 0.4, 0.95, 1.45, 2.2, 2.3, 2.75, 2.95,3.1, 3.3, and 3.4 (all e-4 N-m/rad) can be used, and in one specific example, a spring stiffness of 2.75e-4 N-m/rad can be used.

FIGS. 5A-5C show an energy harvester device 500 in accordance with an example of the present disclosure. The energy harvester device 500 can comprise a support structure 502 that can be generally circular shaped disk or plate comprised of a rigid material, such as iron, steel, metal alloy, aluminum, composite, etc. An eccentrically weighted rotor 504 can be rotatably coupled to a shaft 520 coupled to or extending from the central area of the support structure 502 (see FIG. 5B). A pair of ball bearings 524 (or at least one bearing) can rotatably couple the shaft 520 to the eccentrically weighted rotor 504. Further to this rotation interface, the eccentrically weighted rotor 504 can comprise a central rotor body 526 interfaced to the ball bearings 524 to facilitate rotation of the eccentrically weighted rotor 504. The eccentrically weighted rotor 504 can further comprise a first metal backing plate 512a, an opposing second metal backing plate 512b, an annular support frame member 513, a mass 505, and an outer housing 517. The first and second metal backing plates 512a and 512b can be attached to each other via the annular support frame member 513 and the mass 505 (e.g., tungsten, brass), which can each have a radial profile that corresponds to the circular perimeters of the first and second metal backing plates 512a and 512b.

As best shown in FIG. 5B, a stator substrate 528 (e.g., PCB board) can be attached or supported by an annular flange 529 of the support structure 504, and can support or comprise a plurality of stator coils 530, which can each be received or supported by coil support openings 532 formed radially in an array around a perimeter of the stator substrate 528.

The energy harvester device 500 can comprise a rotor movement limiter mechanism, such as a rotational coil spring 506 having one end 534a coupled to a hole in the central rotor body 526 of the eccentrically weighted rotor 504, and the other end 534b coupled to a hole in the second metal backing plate 512b. The rotational coil spring 506 can have one or more coil turns, or even less than one coil turn, and still be defined as a rotational spring. As similarly and generically exemplified in FIGS. 1-2C, the rotational coil spring 506 can be operable to maintain or bias the eccentrically weighted rotor 504 in an upward position with respect to gravity when worn by a user in a standard use orientation. This includes the functionality and benefits described herein regarding incorporating a spring in this manner to maintain or balance the eccentrically weighted rotor 504 in an upward position to provide an unstable equilibrium position of the eccentrically weighted rotor 504.

In one example, the eccentrically weighted rotor can at least partially define the transducer, and the transducer can comprise a rotor body and a plurality of alternating rotor magnets supported by the rotor body. The energy harvester device can comprise a first coil support body supporting a first plurality of stator coils, such that the plurality of alternating rotor magnets are disposed above the plurality of stator coils to harvest electrical energy in response to rotation of the eccentrically weighted rotor. For example, the energy harvester device 500 can further comprise a plurality of permanent rotor magnets 536 (having alternating polarity) attached to an inner planar surface of the first metal backing plate 512a, such that the permanent stator magnets 536 are situated between respective stator coils 530 and the first metal backing plate 512a, as best shown in FIG. 5C. This configuration provides a first air gap A3 located between the permanent rotor magnets 536 and respective stator coils 530, and a second air gap A4 between the stator coils 530 and the second metal backing plate 512b. Third and fourth air gaps Al and A2 are formed between metal backing plate 512a and housing 517, and metal backing plate 512b and support structure 502. Thus, a transducer 548 of the device 500 can include only four air gaps (i.e. Al, A2, A3, A4) between the permanent rotor magnets 536 and the stator coils 530 and between metal backing plates 512a/512b, support structure 502 and housing 517, which maximizes an electrical damping value and minimizes a profile size of the energy harvester device. This provides a relatively thin, compact energy harvester device 500 because of the reduction of air gaps being just two air gaps.

The transducer 548 can include or comprise a number of components that cooperate to transfer and harvest electrical energy from the energy harvester device 500, such as the magnets 536, the backing plates 512a and 512b, and the coils 530. Therefore, as the permanent rotor magnets 536 and the first and second metal backing plates 512a and 512b rotate relative to the stator substrate 528 and the stator coils 530, this generates an electromagnetic damping effect that converts mechanical energy to electrical energy via induction, which is then transferred from the stator coils 530 (in series) to an electrical load.

In one example, a controller and switches (see e.g., FIG. 4D) can be operably coupled to the plurality of rotor coils 530 to control switching of at least one pair of opposing rotor coils 530 for facilitating variable electromagnetic damping, similarly as described above.

FIGS. 6 A and 6B show an energy harvester device 600 in accordance with an example of the present disclosure. The energy harvester device 600 can comprise a support structure 602 comprising a first housing portion 603 a and a second housing portion 603 b that each have similar, circular shaped profiles, and that together define a cavity area 607 for housing a number of components therein. A cover plate 609 can be fastened to the first housing portion 603a for enclosing the components therein (only shown in FIG. 6A). An eccentrically weighted rotor 604 can be rotatably coupled to a shaft 620 that is coupled to or extending from the central area of the second housing portion 603b (FIG. 6B). A pair of ball bearings 624 (or at least one bearing) can rotatably couple the shaft 620 to the eccentrically weighted rotor 604. Further to this rotational interface, the eccentrically weighted rotor 604 can comprise a central rotor body 626 interfaced to the ball bearings 624 to facilitate rotation of the eccentrically weighted rotor 604 relative to the shaft 620 and the support structure 602. The eccentrically weighted rotor 604 can further comprise a first metal backing plate 612a and an opposing second metal backing plate 612b attached to each other by the central rotor body 626. A pair of masses 605a and 605b (e.g., tungsten, brass) can be attached to respective perimeter portions of the first and second metal backing plates 612a and 612b, such that the masses 605a and 605b mirror each other.

A stator substrate 628 (e.g., PCB board) can be attached to and supported between the first and second housing portions 603a and 603b of the support structure 602, and can support or comprise a plurality of stator coils 630, which can each be received or supported by coil support openings formed radially in an array around the stator substrate 628. The energy harvester device 600 can comprise a rotor movement limiter mechanism, such as a rotational coil spring 606 having one end 634 coupled to a support collar 627 attached to the shaft 620, and the other end (not shown) of the rotational coil spring 606 coupled to the second metal backing plate 612b (or optionally to the central rotor body 626). As similarly and generically exemplified in FIGS. 1-2C, the rotational coil spring 606 can be operable to maintain or bias the eccentrically weighted rotor 604 in an upward position with respect to gravity when worn by a user in a standard use orientation. This includes the functionality and benefits described herein regarding incorporating a spring in this manner to maintain or balance the eccentrically weighted rotor 604 in an upward position to provide an unstable equilibrium position of the eccentrically weighted rotor 604.

The energy harvester device 600 can further comprise a first plurality of permanent rotor magnets 636a (having alternating polarity) attached to respective openings of an upper rotor section 639a of the central rotor body 626, and a second plurality of permanent rotor magnets 636b (having alternating polarity) attached to respective openings of a lower rotor section 639a of the central rotor body 626. In this configuration, the stator coils 630 are situated between respective first and second pluralities of permanent rotor magnets 636a and 636b, as best shown in FIG. 6B.

A transducer 648 can include or comprise a number of components that cooperate to transfer and harvest electrical energy from the energy harvester device 600, such as the rotor magnets 636a and 636b, the backing plates 612a and 612b, and the stator coils 630. Therefore, as the eccentrically weighted rotor 604 rotates (including the permanent rotor magnets 636a and 636b, and the first and second metal backing plates 612a and 612b) relative to the stator substrate 628 and the stator coils 630, this generates an electromagnetic damping effect that converts mechanical energy to electrical energy via induction, which can then be transferred from the stator coils 630 (in series) to an electrical load.

In one example, a controller and switches (e.g., FIG. 4D) can be operably coupled to the plurality of rotor coils 630 to control switching of at least one pair of opposing rotor coils 630 for facilitating variable electromagnetic damping, similarly as described above. A device was formed consistent with FIG. 6A-6B and power data was collected from ten human subjects walking or jogging on a treadmill. FIG. 6C is a graph showing power results for these ten subjects walking at 2.5 mph. FIG. 6D is a graph showing power results for these ten subjects walking at 3.5 mph. FIG. 6E is a graph showing power results for these ten subjects jogging at 5.5 mph. Notably, power collected under walking conditions was dramatically higher for the sprung rotor, while jogging results exhibited only modest improvements using a sprung rotor harvester device of FIG. 6 A.

FIGS. 7A-7C show an energy harvester device 700 in accordance with an example of the present disclosure. The energy harvester device 700 can comprise a support structure 702 comprising a first support plate 703a (a circular shaped disk or plate) that can be bolted or fastened by fasteners 711 to an opposing second support plate 703b, which can be an irregular or triangular-like shaped plate or disk. As best shown in FIGS. 7B and 7C, an eccentrically weighted rotor 704 can be attached to a shaft 720 that is rotatably coupled to and supported by the first and second support plates 703a and 703b. In this manner, a pair of ball bearings 724a (or at least one bearing) can rotatably couple a lower end 721a of the shaft 720 to the second support plate 703b, while another ball bearing 724b rotatably couples an upper end 721b of the shaft 720 to the first support plate 703a. Here, the eccentrically weighted rotor 704 can comprise a central rotor body 726 having a central aperture 727 that is secured or attached to a portion of the shaft 720 between the first and second support plates 703a and 703b.

The energy harvester device 700 can further comprise a plurality of permanent rotor magnets 736 (having alternating polarity) attached to respective support openings of the central rotor body 726. A first metal backing plate 712a can be attached to an inner surface of the first support plate 703a, and an opposing second metal backing plate 712b can be attached to an inner surface of the second support plate 703b. Each of the metal backing plates 712a and 712b can support respective first and second pluralities of stator coils 730a and 730b situated on either sides of the permanent rotor magnets 736.

The energy harvester device 700 can comprise a rotor movement limiter mechanism, such as a rotational coil spring 706 having one end 734a fixed to the first support plate 703 a, and the other end 734b attached to an upper end of the shaft 720, which is attached to the central rotor body 726. As similarly and generically exemplified in FIGS. 1-2C, the rotational coil spring 706 can be operable to maintain or bias the eccentrically weighted rotor 704 in an upward position with respect to gravity when worn by a user in a standard use orientation. This includes the functionality and benefits described herein regarding incorporating a spring in this manner to maintain or balance the eccentrically weighted rotor 704 in an upward position to provide an unstable equilibrium position of the eccentrically weighted rotor 704.

A transducer 748 can include or comprise a number of components that cooperate to transfer and harvest electrical energy from the energy harvester device 700, such as the magnets 736, the backing plates 712a and 712b, and the coils 730a and 730b. Therefore, as the permanent rotor magnets 736 rotate relative to the stator coils 730a and 730b, this generates an electromagnetic damping effect that converts mechanical energy to electrical energy, which can be transferred from the stator coils 730a and 730b (in series) to an electrical load.

In one example, a controller and switches (see e.g., FIG. 4D) can be operably coupled to the plurality of stator coils 730a and 730b to control switching of at least one pair of opposing stator coils 730a and 730b for facilitating variable electromagnetic damping, similarly as described above.

FIGS. 8 A and 8B show an energy harvester device 800 in accordance with an example of the present disclosure. The energy harvester device 800 can comprise a support structure 802, which can each be circular shaped disk or plate having a cavity for housing components therein. An eccentrically weighted rotor 804 can be fixed to a shaft 820 that is rotatably coupled to the support structure 802 by bearings 824. A rotational coil spring 806 can be coupled on one end to the support structure 802, and coupled on the other end to the eccentrically weighted rotor 804, for maintaining or balancing the rotor 804 in a generally upward position with respect to gravity when worn by a user in a standard orientation. The spring 806 can have the same functionality and advantages as further discussed in the above examples.

The eccentrically weighted rotor 804 can comprise a central body portion 812a formed generally as a circular body portion, and can comprise a peripheral body portion 812b that extends outwardly from the central body portion 812a in a half circle or half moon. One or more masses 805 can be attached to a peripheral surface of the peripheral body portion 812b, thereby generated a rotor that is eccentrically weighted. A plurality of rotor magnets 836a can be attached radially around a surface of the central body portion 812a, and can be configured as cube or cuboid shaped magnets having a positive polarity, for instance, facing inwardly toward each other and toward the shaft 820.

A plurality of piezoelectric beams 829 can be arranged radially around the eccentrically weighted rotor 804 and spatially separated from each other. The piezoelectric beams 829 can be thin, flat panels comprised of piezoelectric material, and can be fixed or sandwiched to the support structure 802 by a support frame 811 that is fastened to the support structure 802. In this manner, the piezoelectric beams 829 extend inwardly toward a center of the eccentrically weighted rotor 804, and envelope a majority of the two dimensional space about the area to which they are coupled, which maximizes power output. A plurality of stator magnets 836b can be attached to inner surfaces at ends of respective piezoelectric beams 829. The plurality of stator magnets 836b can be situated inwardly relative to respective rotor magnets 836a, so that rotation of the eccentrically weighted rotor 804 caused the rotor magnets 836a to rotate in laterally outside of the stator magnets 836b, but generally on the same plane. The stator magnets 836b can have a north polarity that faces inwardly toward the rotor magnets 836a. In this way, as each of the rotor magnets 836a pass laterally along the stator magnets 836b during rotation of the eccentrically weighted rotor 804, the respective stator magnets 836b are repelled laterally by and away from the rotor magnets 836a (due to the polarity arrangement), which causes a force on the piezoelectric beams 829 that deflects or bends the respective piezoelectric beams 829 outwardly, which converts mechanical motion to electrical energy due to the piezoelectric effect/nature of the piezoelectric beams 829. Although not shown, the piezoelectric beams 829 can be electrically coupled together in series and to an electrical load, such as a battery or electronics device for harvesting energy, as should be readily appreciable by those skilled in the art. Thus, a transducer 848 of the energy harvester device 800 can include the piezoelectric beams 829, and the rotor and stator magnets 836a and 836b, and other circuitry that may not be shown but that is well known in the art for transferring and harvesting electrical energy.

In one example, the transducer can comprise a magnetic piezoelectric plucking mechanism, and the eccentrically weighted rotor can comprise at least one magnet, such that rotation of the eccentrically weighted rotor causes the at least one magnet to repulse a corresponding magnet of the magnetic piezoelectric plucking mechanism, thereby causing deflection of at least one piezoelectric beam to harvest energy. For example, the plucked piezoelectric beams disclosed herein can be the beams as further described in T. Xue and S Roundy, "Analysis of Magnetic Plucking Configurations for Frequency Up-Converting Harvester," Journal of Physics: Conference Series 660 (2015) 012098, which is incorporated herein by reference.

FIGS. 9 A and 9B illustrate an energy harvester device 900 that can be incorporated with an electronics assembly, such as a wearable electronics device, for powering components and/or a battery source of the wearable electronics device. The energy harvester device 900 can comprise a reference frame or support structure 902, and an eccentrically weighted rotor 904 rotatably coupled to the support structure 902 by a shaft 920. The eccentrically weighted rotor 904 can include a mass (not shown) (e.g., like 105, 405, 505, etc.) disposed around a radial section of the eccentrically weighted rotor 904. In this alternative, the rotor movement limiter mechanism can be a set of magnets (e.g. either permanent or electromagnetic) which bias movement and position of the eccentrically weighted rotor. The energy harvester device 900 can comprise a rotor movement limiter mechanism, such as a magnetic latching system 906 that can comprise first and second stator magnets 908a and 908b attached to the support structure 902 and radially spaced from each other. The magnetic latching system 906 can further comprise first and second rotor magnets 910a and 910b attached to the eccentrically weighted rotor 904 at respective corresponding positions relative to the first and second stator magnets 908a and 908b. The first and second stator magnets 908a and 908b have an alternating polarity relative to respective first and second rotor magnets 910a and 910b, so that when the eccentrically weighted rotor 904 rotates to clockwise, as in FIG. 9A, the first rotor magnet 910a is magnetically attracted to and latched to the first stator magnet 908a. Upon the opposite rotation in the counterclockwise rotation, and with sufficient rotational force or torque acting on the eccentrically weighted rotor 904, the first rotor and stator magnets 910a and 908a can be un-latched from each other upon the eccentrically weighted rotor 904 exceeding an un-latching torque threshold. This is because first rotor and stator magnets 910a and 908a are tuned to particular magnetic forces based on the mass of the eccentrically weighted rotor 904 and the degree of rotational freedom of the rotor 904. These factors dictate the value of the designed un-latching torque threshold. In response to being un-latched, the eccentrically weighted rotor 904 can rotate relatively quickly to the left (FIG. 9B) because of the potential energy stored in the latched magnets 908a and 910a being released upon un-latching. Such "quick" rotational movement can generate more electrical energy than a rotor moving slower, because of the increase in electrical damping, in cases where an electromagnetic transducer is incorporated with the system of FIGS. 9A and 9B. Thus, the eccentrically weighted rotor 904 can quickly rotate counterclockwise to the point at which the second rotor magnet 910b is magnetically attached or latched to the second stator magnet 908b, which are also similarly tuned as the other rotor and stator magnets 910a and 908a. Thus, the rotor 904 can oscillate between these two positions shown in FIGS. 9 A and 9B, as being limited in rotation by the position of the stator magnets 908a and 908b.

In an alternative example, the polarity of the rotor magnets (e.g., 910a and 910b) can be flipped, so that they provide a repulsive force (and not a latching/attractive force) to respective stator magnets. In this way, the eccentrically weighted rotor can "bounce" off of respective stator magnets when approaching the relevant stator magnet, which can increase the amplitude of the oscillations of the rotor.

In an alternative example, the stator magnets can each be replaced with a compliant stop, such as an elastic puck or other compliant element attached to the support structure. In this way, when the eccentrically weighted rotor rotates to such compliant stop, it can bounce off of the compliant stop and swing over to an opposing compliant stop. This can be repeated during motion of the user to oscillate the eccentrically weighted rotor to generate electrical power.

The various transducers exemplified herein can be advantageous over prior transducers because the presently disclosed transducers do not require or utilize the use of a gear train or other complex component to increase the rotational speed of the rotor/transducer. The incorporation of a rotational spring in the examples described herein can be incorporated with other suitable transducers, such as small electromagnetic generators, other piezoelectric transducers, and variable capacitance transducers. As noted above, the present energy harvester devices can significantly increase the amount of power that can be generated from a wearable electronic device as compared to the prior art, particularly one worn on the wrist, upper arm, torso, belt, leg, ankle, or foot. Some examples include self-powering wearable activity trackers, health related sensors, etc., and any other wearable device that requires a power source. In some example, wearable devices that may only include one or two purposes, thereby requiring less power (as compared to a high-performance smart watch that requires a relatively high amount of power), can include certain activity trackers (i.e., exercise tracking, wildlife trackers, etc.), and emerging wearable health sensors (e.g., glucose sensors, heart rate monitors, blood oxygen sensors), and air quality monitors, or the like. Such devices may require a very low power output, typically less than 500 μ\Υ and often from 100-200 μ\Υ can be particularly suitable devices to incorporate this system. However, the examples discussed herein can be used in other devices that require power.

In some examples, a particular energy harvester device can be configured to reduce the cogging torque to very near zero. For example, the interaction of the stator and rotor magnets of the device shown in FIG 8A and 8B can cause a cogging, or detent, torque. This torque is generally not beneficial to the operation of the device. Therefore, the spacing of the magnets can be chosen to minimize the effect of this cogging torque. For the devices with arrays of magnet and coils (i.e. FIG 4A, 5A, 6A, and 7A), the cogging torque is minimized by creating a structure in which there is no relative emotion between the one or more magnet arrays and any other magnetic material.

In some examples, a particular energy harvester device can be used with shipping tracking devices for asset tracking. Thus, while cargo is being moved or transporting, it experiences continuous or periodic movement or vibrations, which can cause oscillation of an eccentrically weighted rotor balanced by a rotational spring, for example.

Other applications include using a particular energy harvester device as a coupled inductive coil device for transferring power inductively. For example, rather than generating power as a result of motion, the coils can couple to a nearby external coil that creates an oscillating magnetic field. The coils in the energy harvester can couple to that field and generate power from the external coupled inductive coil. The coils in the energy harvester can have a self-resonance frequency. If the external transmitting coil is tuned to operate at the same resonance frequency, then the power generated can be maximized. Thus, although the energy harvester would not be designed specifically as a wireless power transfer device, it could also operate as such a device.

In some examples, a particular spring can be a torsional shaft, such as one made of a polymer or elastic material, so that the eccentrically weighted rotor is balanced or maintained in an upward position. In some examples, one or more linear springs can be arranged between the eccentrically weighted rotor and a support structure to balance the eccentrically weighted rotor in an upward position with respect to gravity.

In some examples, an electrostatic transducer can be incorporated. For example, the electrostatic transducer can contain a permanently charged dielectric material (i.e., an electret) coupled to a plurality of electrodes which are supported by the stator. The moving rotor can contain matched electrodes. Capacitance between the electrodes on the stator and the electrodes on the rotor changes as the rotor moves relative to the stator and the matching electrodes become misaligned and then re-aligned. As the capacitance changes, charge to and from the electrodes. This charge can flow through an external load circuit thus creating an energy harvester.

The foregoing detailed description describes the invention with reference to specific exemplary embodiments. However, it will be appreciated that various modifications and changes can be made without departing from the scope of the present invention as set forth in the appended claims. The detailed description and accompanying drawings are to be regarded as merely illustrative, rather than as restrictive, and all such modifications or changes, if any, are intended to fall within the scope of the present invention as described and set forth herein.